Question: Solve for $x$ and $y$ using substitution. ${5x-3y = -5}$ ${x = -y-9}$
Solution: Since $x$ has already been solved for, substitute $-y-9$ for $x$ in the first equation. ${5}{(-y-9)}{- 3y = -5}$ Simplify and solve for $y$ $-5y-45 - 3y = -5$ $-8y-45 = -5$ $-8y-45{+45} = -5{+45}$ $-8y = 40$ $\dfrac{-8y}{{-8}} = \dfrac{40}{{-8}}$ ${y = -5}$ Now that you know ${y = -5}$ , plug it back into $\thinspace {x = -y-9}\thinspace$ to find $x$ ${x = -}{(-5)}{ - 9}$ $x = 5 - 9$ ${x = -4}$ You can also plug ${y = -5}$ into $\thinspace {5x-3y = -5}\thinspace$ and get the same answer for $x$ : ${5x - 3}{(-5)}{= -5}$ ${x = -4}$